Process of making boron carbide containing aluminum, and products thereof



Patent d. My??? 12-5 m aterial is a horide as well as acarbideand itcan j ust as 2,746,133 truly b e led carbonboride and'design ed CB4. It can i .haliei e 9: O q filid moo-ass F BORON' CARBIDECON- iTAlNlNG ALUMINUM, AND JPRODUQTS :TIIEREOF ilid int -tlaprr tz lia ara Fa tlQn a t Can da, s i o toNorton Company, Worcester, Mass., a corppratign ..,Ma ahu$" a i iorp vi la compo t w c a h r yn esize If e d ty ay l b ma fl ompar iv y .i ow as t anl swl s composi o c b vH I1 2 nt lhar g tarticles a dalso used for various other purposes sueh as ar1,abrasive. Anotherobject of the iinvention is 3 rovid ts meri li no le an t b bl d s and ,xnt' inhe i etu art cl h a mp l bl de ff .haadfinasfit amiabradye. a dblast nq t g w r dra ;iy disam l 'linetsrsyli de elinfir h ri tan filly- ;tl ias Whbhslwu fi m 1 r bi twh q rq eh #1 a twa rt an hprq tca b d .B enqthe bieq of the jnventionis to provide a cqmpositionawhich is ma ln bor n car i b Whih s stfopgert flunk-1 1 9 r n terialwhich is notonly extremely hard and of adequate strength but which is also quite refractory. Another obl pfthe invention is toprovidea material ofthen ature i icated which'isnon-reactive with most other materials. Other objects will be in part obvious or in part pointed out hereinafter.

Boron carbidemade in accordance withRaymond R. g Ridgyv ays Patent No. 1,897,214is saidito be BgC gbut inl'accordance with his l atent -No. 214L617 ahomolgerregus composition consisting 'o f xBrC+yB can befiriade "and as a matter effect, carrying out'the process of -No. 1,897,214 as more specifically taught in his-Patent No. 2,155,682 results in the manufacture of some material that has more boron in it .than is in ,boronucarhide .twhichmis r trictly,,BC. In such material the excess boron is in solid sol1 tion but the boron isreaetable as such. Such material has frequently been referred to as boron rich .lmmn. carbideand. is high grade material..which can be itm l into P t nt .v when! astpieqesmqlsle Qut of pure B4C provided thereis not .too great anexcessgf boron (but if there is excess of boron over B4C it will reactwith the graphite to pick up additional carbon during emolding ifthere" is noelernent present except carbon and -bo r on) i "Likewise, when manufacturing boron carbide in accordance witha Patent ;No. 2,155,682 some! material is found tocontain less boron than is presentQiripurelBgC and-provided the -deficiency is not too greatthis al so is -high --grade 'material. Accordingly commerciallyihigh .agrade boron carbide which can be molded into pieces of ;close.\to'=the theoretical-density and of a hardness greater :athaniany other now known :material :except. xliamondlis moterestrieted .-,to'- literally and exactly :='B4C but includes matei ial;ranging all;-theawayfromgBmC tQsJBaaC. :Thjs

counts for the fact that rnaterial all the way 5 to B5.4C is substantially'thesame. For the molding of tlie li'a'rdest and strongest pieces out of ,this material various l ots are analygedi and then a batch is made up which, "on the average, comes very closeto-'B4C,and of course the var ious components bf the batch are-thoroughly mixed. The-best grade pieces Qmade-in-thismanner, molded in thefur'nace 'of Ridgways U. S. "Patent-2,125,588,- have an average modulus of "rupture of 40,000-pounds per -square inch. 'Pieces thus jmade have a a hardness greater; than: any 'other fab'ricated pieces of-anything (since diamond cannotbe fa-bricated) and highly polished surfaces can be formed on them and for many purposes their strength is adequate, but for enn tatm arwne e hi lmq al a P 2 =4QQ pou'nds per sguareinch leaves someth I e a he i d j a' b wn 2 a ha ing di'i lus ofl rupture bras much as p undsiip square inch. ,Tnis'. 1h ;eri;t1 "is;scih arty as ,l

lion 2 carbide Iv BgC that j for 2 awfu re i it Kn idetect anyditferencrbetw e fsa' id t i it a v n uman' e ih 'mamaame Hf 1 sample Lo blPfQn car ide a's;is represented: by 'BeCfand in fact I' b e gl am; rial (which, on theaveir s5 rmp aam yieldfinalmoldedfpiecesha pg 5% I by weight of aluminum; on the total 9 b0 ammmmum inqwbu w amthe hes gpi w bi m 7 1 157 ffill lll t .flw st d ab y st o pi qt i hi lb b .hav n nq lum iu The actual amount of aluminum to a frorn 10% to 20% on the total. of a 'garh deandth z fis o h p ytfil neanai riroqee jt .tv Q i t Half 5 how to make my improved article's. 'After thoroughly mixing the boron carbide powder and the aluminum P w .91 9 ;t rqs tinamateria i -amht a and place the m'old in a molding furna s ch a'sa furnaee constructedaccording to Patent No. 25%588 a ii d tli'en mold the-material in-aecordance with -the procedgre set forth in--Ridgwa-y-s U.-S;--Patent-Now2,027fi86. Standard rnoldingpressure of-Z-SOO pounds per square inchis'preferably used, but-; f orth;is-first molding l can use lower pressures,v as low-even as 500 pounds -per-square inh.

The temperature of the mold should be carried to above 1800 C. and preferably to 1850 C. but not above i. ?0 .1 11312 19 JQBPEWHE isnth r nrettmm 1800 C. to 1900 C.

It is rather surprising that Lean make this boron carbide containing aluminum in this 'manner since aluminum ltaetfisfi t C-ian boi sd t-l itl C- aBut Llraye in n TABLE I I Satisfactory particle size of molding powder Size: Percentage by weight 1 micron to 2 microns 10 2 microns to 3 microns 10 3 microns to 5 microns 25 -5 microns to 8 microns L. 45 8 microns toll microns 5 11 microns to 15 microns .7 5

It will now be seen why the amount of aluminum added to the boron carbide is greater than the amount of aluminum in the finished pieces. Some ofthe aluminum was used up in forming aluminum carbide which was eliminated by the ball milling with water. It will further be seen that the amount of aluminum to add to the boron carbide is not critical for the following reasons. After the ball milling with water the material is analyzed. Obviously it will contain from 2% to 5% of aluminum or more or less. If it contains from 2% to 5% of aluminum it is ready for final molding. If it contains more than 5% aluminum simply add enough boron carbide containing no aluminum to lower the aluminum content of the whole mixture to the desired percentage. If, after ball milling with water, the material contains less than 2% of aluminum rnake up another batch adding'enough 'more aluminum to the boron carbide than in the previous run to be certain to obtain more than 5% of aluminum. Then after ball milling with water and afteranalysing the second batch for aluminum, the two batches can. be

mined'in calculated proportions to give the desired percentage of aluminum (between 2% and 5%) in the mixture. Any such mixing should be very thoroughly done- 7 It is not necessary, in carrying out my invention, to use very pure aluminum. I have used commercial aluminum paint powder having the following analysis.

TABLE II I Analysis of aluminum powder used in this invention 7 Thus a considerable amount of alumina can be tolerated but' other impurities should be kept to a low figure.

'vention or if so in what proportion.

polished samples of my aluminum-carbon boride com- Probably 15% of alumina in the added powder is a practical maximum with not more than 1% of matter other than Al and A1203. Some of the alumina is undoubted- 1y reduced to aluminum during the two molding stages. but X-ray analysis showsthat some alumina appears in f the final pieces where powders such as those analyzed in-Table II are used. Alumina in the final pieces up to 2% by weight can be tolerated. Other elements and compounds other than aluminum, boron and boron carbide can be tolerated up .to 1% by weight. The a1uminum which is present from 2% 'to 5% is other than that inAlzQs. I

There areitwo boridesof'aluminum recognized in the literature, namely aluminum boride A182 and aluminum boride A1B12. these is formed in making pieces according to. my inposition showed the presence of two phases other than boron carbide, i. e. three phases in all. I These two other phases seemed to be quite transparent and hence it is likely that one ,was AlBz and the other was AlBiz. Accordingly I willhave to say that my composition contains from 2% t0 5% by weight of aluminum'additional tothe aluminum in alumina A1203.

After the molding powder containing 2% to 5% by weight of aluminum apart from any alumina,'having not over 2% of alumina and not over 1% of matter apart from the boron carbide (which can be anywhere fromv vBmC to Bsl aC) alumina and other aluminum matter has been thus prepared, it is charged into a graphite mold (see U. S. Patents Nos. 2,027,786; 2,121,744; 2,125,588; 2,150,884; 2,522,046; 2,535,180 and 2,473,476 for various mold shapes which .can be used although the invention, j is not limited to the use of any shape of gmold), the

mold is then charged into a pressure furnace suchas the one illustrated in Ridgways Patent No. 2,125,588, and;

then the furnace tube is heated and the pressure is applied, the temperature being run up to between 1850 .C. and 2325 C. but preferably between about l900' C. and

, 1950 C. and at the top temperature I prefer to use stand-f ard pressure, of 2500 pounds per square inch and anyway the pressure should rise to at least 1500 pounds.

per square inch. It is desirable to hold the pressure until the furnace tube temperature has dropped to 1600" o C. as otherwise, in some-cases, the article or articles may 7 crack. v

Articles made in accordance with this invention having percentage of aluminum as defined herein according to the following table have had average modulus of j They are superior artirupture according to the table. cles if they have a modulus of rupture of at least 43,000 pounds to the square inch.

,TABLE IV Average Mod- Percentage of Aluminum by Weight Pounds per Square Inch While I prefer to make: the composition in a molding.

furnace as described nevertheless the composition can be made in a resistance furnace such as the furnace illustrated in Patent No. 2,123,158. Control of the process is a little more difiicult in this furnace of Patent No.

2,123,158 than it is in the tube furnace of 'Patent No.

.ducing; The advantage, however, of using a furnace 1 such as that shown in Patent No. 2,123,158 is that larger yields can'be obtained. For obtaining stilllarger yields I cannot say whether either or both of Examination of ulus 0t Rupture I V 5 an arc furnace such as shown in Ridgways Patent No. 2,285,837 could be used but here again it will be found that conditions are still more difficult to control in such a furnace.

It will thus be seen that there has been provided by this invention a composition and articles of boron carbide containing aluminum and a process for making the same in which the various objects hereinabove set forth together with many thoroughly practical advantages are successfully achieved. As various possible embodiments might be made of the mechanical features of the above invention and as many changes might be made in the embodiments above set forth, it is to be understood that all matter hereinbefore set forth is to be interpreted as illustrative and not in a limiting sense.

I claim:

1. A composition of matter essentially consisting of boron carbide having from 2% to 5% of aluminum additional to the aluminum in alumina, said composition having not over 2% of alumina and not over 1% of matter apart from boron carbide, alumina and the said 2% to 5% of aluminum additional to the aluminum in alumina, said boron carbide having been reacted with said alumihum and said aluminum being completely dispersed throughout said boron carbide.

2. An article of manufacture essentially consisting of boron carbide having from 2% to 5% of aluminum additional to the aluminum in alumina, said article having not over 2% of alumina and not over 1% of matter apart from boron carbide, alumina and the said 2% to 5% of aluminum additional to the aluminum in alumina, said boron carbide having been reacted with said aluminum and said aluminum being completely dispersed throughout said boron carbide, said article being compacted to a dense hard mass having a hardness greater than 9 on Mohs scale and a modulus of rupture of at least 43,000 pounds per square inch.

3. Process of making boron carbide containing aluminum which comprises adding to boron carbide which analyses between Bs.sC and 135.4C, aluminum in powder form containing not over 15% of alumina and not more than 1% of matter other than aluminum and alumina, mixing, placing the mixture of boron carbide and aluminum in a graphite mold, and heating to a temperature of between 1800 C. and 1900 C. while maintaining a pressure on the mold of at least 500 pounds per square inch, thereby producing a solid piece of the material, then crushing the piece and ball milling the fragments with water to powder of a particle size of at least as small as 15 microns, thereby also eliminating aluminum carbide from the material, then making a batch of powder containing from 2% to 5% by weight of aluminum additional to the aluminum in alumina, the remainder boron carbide and not over 2% of alumina and said batch containing not over 1% of matter apart from boron carbide, alumina, and said 2% to 5% by weight of aluminum additional to the aluminum in alumina, by mixing boron carbide powder containing more than the required amount of aluminum within said range of 2% to 5% made as aforesaid with boron carbide powder containing less than said required amount of aluminum, charging said batch into a graphite mold, and then heating said batch in said mold to between 1850" C. and 2325 C. under a pressure of at least 1500 pounds per square inch.

References Cited in the file of this patent UNITED STATES PATENTS 270,384 Call Jan. 9, 1883 2,077,345 Van der Pyl Apr. 13, 1937 2,077,366 Milligan Apr. 13, 1937 2,200,258 Boyer May 14, 1940 

1. A COMPOSITION OF MATTER ESSENTIALLY CONSISTING OF BORON CARBIDE HAVING FROM 2% TO 5% OF ALUMINUM ADDITIONAL TO THE ALUMINUM IN ALUMINA, SAID COMPOSITION HAVING NOT OVER 2% OF ALUMINA AND NOT OVER 1% OF MATTER APART FROM BORON CARBIDE, ALUMINA AND THE SAID 2% TO 5% OF ALUMINUM ADDITIONAL TO THE ALUMINUM IN ALUMINA, SAID BORON CARBIDE HAVING BEEN REACTED WITH SAID ALUMINUM AND SAID ALUMINUM BEING COMPLETELY DISPERSED THROUGHOUT SAID BORON CARBIDE. 